1. Field of the Invention
The present invention relates to the field of guidewires, and more particularly to a blood filter guidewire device to be used in percutaneous carotid angioplasty procedures for treatment of carotid artery stenosis and any other hollow conduit disorders.
2. Description of the Related Art
Carotid artery stenosis is a narrowing of the carotid artery due to build-up of atheromatous plaque. Carotid artery stenosis is the most common cause of stroke and stroke is the third leading cause of death and the number one cause of long-term disability in the United States. The standard treatment for patients with carotid artery stenosis is carotid endarterectomy (CEA). CEA is a surgical procedure that involves open exposure and incision of the carotid artery followed by removal of the atheromatous plaque. Currently, physicians perform 120,000 CEA procedures annually in the United States.
A newer procedure called percutaneous transluminal angioplasty (PTA) of the carotid artery has been advocated as an alternative to CEA for the treatment of carotid artery stenosis. The procedure involves insertion of a balloon tipped catheter into the stenotic region of the carotid artery. The physician inflates the balloon against the stenotic artery wall to dilate the arterial lumen, thereby improving blood flow through the vessel.
PTA may be a viable alternative to and/or possible replacement of CEA. However, preliminary published results of PTA procedures reveal higher stroke/death rates compared to those achieved with CEA. The increased stroke rates result from the dislodgment of intra-arterial embolic material during the angioplasty procedure.
There has been some work done on devices to deal with this situation. For example, U.S. Pat. No. 4,723,549 to Wholey et al. describes a catheter designed to slide over a guidewire for dilating occluded or stenotic blood vessels. The Wholey et al. device is a balloon catheter with a collapsible filter portion. The collapsible filter is deployed by inflating a filter balloon positioned near the distal end of the catheter. The catheter also has a dilating balloon set back proximally from the filter balloon for compressing the stenosis. The collapsible filter device comprises a plurality of resilient ribs secured to the catheter at the distal end of the catheter and extending generally longitudinally toward the dilating balloon. Inflation of a filter balloon pushes the ribs outwardly against the vessel wall to stretch filter material secured to the ribs across the vessel to form a cup shaped trap. This filter is supposed to capture fragments of a stenosis loosened by the dilating balloon. Upon deflation of the filter balloon, the resilient ribs retract against the catheter to retain the trapped fragments during withdrawal of the catheter. In the preferred embodiment of the Wholey et al. device, the proximal ends of the ribs projecting generally toward the dilating balloon are moveably secured to a ring that slides along the outside surface of the catheter. In use, the cup-shaped trap filter is extended and then the dilating balloon is inflated. Blood flow established by deflation of the dilating balloon carries stenosis fragments into the filter.
There are several shortcomings with the Wholey et al. catheter. For example, in the first embodiment, nothing positively moves the ribs and the carried filter to the retracted position against the walls of the catheter. Furthermore, the free ends of the ribs could very well entangle with each other, or possibly damage the vessel walls, and/or inadvertently release captured particles from the trap filter. In the second embodiment, a slideable ring moveably retains proximal ends of the ribs. This second ring is slidably positioned on the outside surface of the catheter. In both embodiments, all the filter components are located to the exterior or on the outside of a rather large catheter. During withdrawal of the catheter, there is a possibility that free proximal ends of the ribs (or the slideable ring) can be caught on the vessel walls and thus reopen the trap filter. Moreover, the Wholey et al. catheter, by integrating the trap filter into the design of the catheter gives a physician less flexibility in where the filter is to be positioned relative to the stenosis. Indeed, it would appear that the excessively complex design of Wholey et al would make the device too large to fit and function within the carotid artery.
U.S. Pat. No. 5,695,519 to Summers et al. discloses a distal intravascular filter for filtering blood and entrapping and retaining embolic debris. The intravascular filter includes a small diameter hollow guide wire or tube capable of percutaneous placement beyond a carotid stenosis. The distal portion of the tube includes a filter mounted thereon. The filter is deployable from a tightly closed configuration to an open circumference for filtering embolic material from the bloodstream. The filter is deployable between open and closed positions by manipulation of an actuating wire extended from the filter and out the proximal end of the tube. An examination of the design would indicate that at least one major problem with the Summers et al. device is that the actuating wires are too thin. Deployment of the filter mechanism requires pushing the actuating wires along a column of about 175-cm in length. The wires cannot support the force necessary to properly deploy the filter because they cannot be made thick enough to perform their function and constrain to the necessary dimensions of the hollow tube or wire. A second problem is that once the filter is deployed, there is no way to assure that the filter will stay open and be secured against the arterial wall. The system relies on the blood flow to keep it open, which may not be sufficient to maintain an open filter, particularly in a stenotic carotid artery. Thirdly, because of a multitude of moving parts, the system would likely be expensive to produce and difficult to assemble, and would likely encountering similar problems of as that of the Wholey et al catheter, including inability to fit all the parts into a tight space.
There accordingly remains a need for a guidewire filter device that can be used in lieu of conventional guideware during percutaneous carotid angioplasty procedures to capture any dislodged intra-arterial embolic material.
One object of the invention is to provide a guidewire filter device that is compatible with current carotid angioplasty balloon catheter systems, viz., can be used in place of conventional guidewires.
Another object of the invention is to provide a guidewire filter device in which filter or mesh material is located inside of the guidewire filter rather than outside the guidewire or catheter shaft to provide a relatively smooth exterior surface. This enables smoother passage of the device within the artery and may decrease the risk of possible fragmentation and subsequent emboli of plaque particles of the stenotic lesion and/or damage to the arterial wall.
Yet another object of the invention is to provide a guidewire filter device including a ribbed cage/basket design that expands to seat against the arterial wall, forming a self-supporting and non-collapsing seal for the filter mesh against the arterial wall. Blood and particles will accordingly be required to travel through the filter mesh rather than around it. While the blood and its components will be able to freely travel through the filter mesh, those particles that are larger than the pore size of the filter mesh, e.g. intra-arterial embolic material, will be prevented from traveling further and will be effectively captured.
A further object of the invention is to provide a guidewire filter device in which the filter is deployed by pulling (rather than by pushing) on an actuating wire allowing use of a thinner wire.
A final object of the invention is to provide a guidewire filter device that is simple in design, involves relatively few parts, is economical to manufacture, and that is reliable and safe in its operation.
These and other aspects of the present invention are afforded by providing a guidewire filter device that comprises a distal filter element contained within a hollow tube/wire housing. The outer diameter of the device will preferably not exceed 0.13 cm (0.050 inches) and even more preferably will not exceed 0.0889 cm (0.035 inches) so as to be compatible with current carotid angioplasty balloon catheter systems. For other uses involving larger hollow conduit disorders, a large size can be utilized. The length of the guidewire will preferably be approximately 150 to 190 cm to allow for catheter exchange during the PTA procedure, but can be of different lengths as required. The filter element or portion is located at the distal end of the device. There are longitudinal slots or xe2x80x9cribsxe2x80x9d located circumferentially around the filter housing. The slots are ideally oriented longitudinally, but can be oriented spirally or in other orientations. Filter mesh material is located inside the filter element and is attached to the inner distal section of the ribs. Alternately, the filter material can be affixed to outer surfaces of the ribs, or can even be sandwiched between the outer ribs and outer rib overlay portions to help secure the filter material in place. In yet a further embodiment, the ribs themselves can be sandwiched by a section of an inner filter material and a section of outer filter material, with the inner and outer filter materials being affixed to inner and outer surfaces, respectively, of the ribs. These inner and outer filters can also optionally affixed at least partly together. In this double material embodiment, the inner and outer filter materials could be made of thinner filter material so that the inner filter material can be made to better fit into the interior surface of the guidewire. An actuating wire attaches to the distal most end of the filter housing and passes through the entire length of the guidewire and out the proximal end. A handle/remote activation device attached to the proximal end attaches to and operates the actuating guidewire.
During a PTA procedure, a physician will use fluoroscopy to steer the guidewire filter device of the invention into place in the carotid artery distal to the stenotic lesion. The physician will then place the balloon angioplasty catheter over the guidewire filter device of the invention. The physician will then use a handle/remote activation device at the proximal end of the device to deploy the filter element or portion at the distal end of the device. The ribs of the filter element will expand into a cage/basket formation. As the cage opens, the folded filter mesh material will open along with the ribs, forming an inverted cup-shaped trap for any embolic material broken loose during the balloon angioplasty procedure. The ribs push against the inner arterial wall, forming a tight seal with the inner arterial wall and the expanded filter mesh covers the opening of the artery. The physician then performs the PTA procedure. After the procedure, the physical will collapse the filter assembly either by withdrawing the guidewire filter housing into the distal balloon catheter tip, and/or by using the handle/remote activation device to release tension on the actuating wire to allow the ribs to reflex back down. Any embolic material resting against the inside of the filter mesh will thus be captured. When the filter element is retracted and closed, any embolic material will be withdrawn from the arteries along with the guidewire filter device of the invention.
The new design of the invention thus has a unique features that render it significantly different and markedly better than other devices used to perform similar functions. The innovations and improvements intrinsic to the current guidewire filter design include the following:
1. The design allows for an accurate and reliable means to activate and deactivate the guidewire filter device.
2. The filter material is preferably stored and operated inside the guidewire filter rather than outside the guidewire or catheter shaft. This allows for maintenance of a smooth exterior, enabling easier movement of the device within the artery and decreases the risk of possible damage to the arterial wall.
3. The ribbed cage/basket design expands to seat on the inner arterial wall, forming a self-supporting and non-collapsing seal for the filter against the inner arterial wall. Accordingly, blood and loose particles will be forced to travel through the filter mesh rather than around it. Those particles that are larger than the filter mesh will be captured and prevented from traveling further by the filter mesh.
4. The filter deploys by pulling the actuating wire rather than pushing on it, allowing use of a narrow gauge wire that is compatible with the inner lumen of the guidewire.
5. The design is simple, reliable, involves relatively few parts, and enables an efficient and low cost process to be used to manufacture the device.